An analysis of the genome of James Watson showed that 16 per cent of his genes were likely to have come from a black ancestor of African descent. By contrast, most people of European descent would have no more than 1 per cent.

“This level is what you would expect in someone who had a great-grandparent who was African,” said Kari Stefansson of deCODE Genetics, whose company carried out the analysis. “It was very surprising to get this result for Jim.”